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| United States Patent |
6,231,956
|
|
Brenner
, et al.
|
May 15, 2001
|
Wear-resistance edge layer structure for titanium or its alloys which can
be subjected to a high mechanical load and has a low coefficient of
friction, and method of producing the same
Abstract
Wear-resistant edge layer for titanium and its alloys which can be
subjected to high loads and has a low coefficient of friction. The
wear-resistant edge layer includes a hard amorphous carbon layer, an
intermediate layer, and a laser gas alloyed layer. The wear-resistant edge
layer may include a 200 to 400 nm thick hard amorphous carbon layer, a 50
to 200 nm thick intermediate layer, and a 0.3 to 2.0 mm thick laser gas
alloyed layer. The laser gas alloyed layer may include precipitated
titanium nitride needles and have a hardness between 600 HV0.1 and 1400
HV0.1. Process for producing a wear resistant edge layer on a substrate.
The process includes forming a laser gas alloyed layer by melting a
surface of a substrate, applying an intermediate layer by Laser-Arc, and
depositing a hard amorphous carbon layer on the intermediate layer by
Laser-Arc.
| Inventors:
|
Brenner; Berndt (Pappritz, DE);
Bonss; Steffen (Zella-Mehlis, DE);
Scheibe; Hans-Joachim (Dresden, DE);
Ziegele; Holger (Lorch, DE)
|
| Assignee:
|
Fraunhofer-Gesellschaft zur Forderung der angewandten Forschung e. V (Munchen, DE)
|
| Appl. No.:
|
147810 |
| Filed:
|
June 14, 1999 |
| PCT Filed:
|
September 12, 1997
|
| PCT NO:
|
PCT/DE97/02071
|
| 371 Date:
|
June 14, 1999
|
| 102(e) Date:
|
June 14, 1999
|
| PCT PUB.NO.:
|
WO98/11272 |
| PCT PUB. Date:
|
May 19, 1998 |
Foreign Application Priority Data
| Sep 13, 1996[DE] | 196 37 450 |
| Current U.S. Class: |
428/216; 427/457; 427/470; 427/532; 427/534; 427/540; 427/577; 428/212; 428/336; 428/408; 428/457 |
| Intern'l Class: |
B32B 009/00; C23C 026/00 |
| Field of Search: |
428/212,408,216,336,457
427/457,470,532,534,540,577
|
References Cited
U.S. Patent Documents
| 4511411 | Apr., 1985 | Brunner et al.
| |
| 4692385 | Sep., 1987 | Johnson.
| |
| 4902359 | Feb., 1990 | Takeuchi et al.
| |
| 4902535 | Feb., 1990 | Garg et al.
| |
| 5009966 | Apr., 1991 | Garg et al.
| |
| 5260107 | Nov., 1993 | Kawamura et al.
| |
| 5326362 | Jul., 1994 | Shetty et al.
| |
| 5366345 | Nov., 1994 | Gerdes et al.
| |
| 5368939 | Nov., 1994 | Kawamura et al.
| |
| 5413641 | May., 1995 | Coulon.
| |
| 5593719 | Jan., 1997 | Dearnaley et al.
| |
| 5605714 | Feb., 1997 | Dearnaley et al.
| |
| Foreign Patent Documents |
| 3917211 | Nov., 1990 | DE.
| |
| 0105835 | Apr., 1984 | EP.
| |
| 0242100 | Oct., 1987 | EP.
| |
| 0246828 | Nov., 1987 | EP.
| |
| 0322812 | Jul., 1989 | EP.
| |
| 0491075 | Jun., 1992 | EP.
| |
| 0592309 | Apr., 1994 | EP.
| |
| 90/14447 | Nov., 1990 | WO.
| |
| 95/26169 | Oct., 1995 | WO.
| |
Other References
Brenner et al., "Mechanical and Tribological Properties of Laser Gas
Ti6A14V", pp. 477-484, presented at the ECLAT '96 (6th European Conference
on Laser Treatment of Materials) (Sep. 16-18, 1996).
H. W. Bergmann, "Thermochemische Behandling von Titan und Titanlegierungen
durch Laserumschmelzen und Gaslegieren", Zeitschrift fur Werkstoffechnik
16 pp. 392-405 (1985). (No Month).
A. Kolitsch et al., "Modification of Laser-Arc DLC Layers by Ion Beams"
Proceedings. International Symposium Trends New Applications on Thin
Films, (Jan. 1, 1993).
|
Primary Examiner: Turner; Archene
Attorney, Agent or Firm: Greenblum & Bernstein, P.L.C.
Claims
What is claimed is:
1. A wear-resistant edge layer for titanium and its alloys which can be
subjected to high loads and has a low coefficient of friction, comprising:
a hard amorphous carbon layer;
an intermediate layer; and
a laser gas alloyed layer.
2. The wear-resistant edge layer of claim 1, wherein the hard amorphous
carbon layer is 200 to 400 nm thick.
3. The wear-resistant edge layer of claim 1, wherein the intermediate layer
is 50 to 200 nm thick.
4. The wear-resistant edge layer of claim 1, wherein the laser gas alloyed
layer is 0.3 to 2.0 mm thick.
5. The wear-resistant edge layer of claim 1, wherein the laser gas alloyed
layer comprises precipitated titanium nitride needles.
6. The wear-resistant edge layer of claim 1, wherein the laser gas alloyed
layer has a hardness between 600 HV0.1 and 1400 HV0.1.
7. The wear-resistant edge layer of claim 1, wherein the intermediate layer
comprises titanium.
8. The wear-resistant edge layer of claim 1, wherein the intermediate layer
consists of titanium.
9. A wear-resistant edge layer for titanium and its alloys which can be
subjected to high loads and has a low coefficient of friction, comprising:
200 to 400 nm thick hard amorphous carbon layer;
50 to 200 nm thick intermediate layer; and
0.3 to 2.0 mm thick laser gas alloyed layer, the laser gas alloyed layer
comprising precipitated titanium nitride needles and having a hardness
between 600 HV0.1 and 1400 HV0.1.
10. The wear-resistant edge layer of claim 9, wherein the intermediate
layer comprises titanium.
11. The wear-resistant edge layer of claim 9, wherein the intermediate
layer consists of titanium.
12. A wear-resistant component which can be subjected to high loads and has
a low coefficient of friction, comprising:
a hard amorphous carbon layer;
an intermediate layer;
a laser gas alloyed layer; and
a substrate comprised of titanium.
13. A process for producing a wear resistant edge layer on a substrate,
comprising:
forming a laser gas alloyed layer by melting a surface of a substrate;
applying an intermediate layer by Laser-Arc; and
depositing a hard amorphous carbon layer on the intermediate layer by
Laser-Arc.
14. The process of claim 11, wherein the substrate comprises one of
titanium and titanium alloy.
15. The process of claim 13, wherein foiling the laser gas alloyed layer
comprises melting tracks in the surface of the substrate with a laser, the
melting taking place in a reactive atmosphere comprising N.sub.2 and Ar.
16. The process of claim 15, wherein the laser has a power density of
1.multidot.10.sup.4 W/cm.sup.2 to 2.multidot.10.sup.5 W/cm.sup.2.
17. The process of claim 15, wherein the reactive atmosphere has an oxygen
partial pressure less than 5 ppm.
18. The process of claim 15, wherein the reactive atmosphere has a nitrogen
content of 40% to 80%.
19. The process of claim 15, wherein an overlap level U is 0.5 to 0.9 where
U=(a-c)/a and where a is a track width and c is a track spacing.
20. The process of claim 13, further comprising after melting the surface
of the substrate, polishing the substrate to a surface roughness less than
or equal to 0.2 .mu.m.
21. The process of claim 13, further comprising cleaning the substrate with
a high vacuum device by ion bombardment.
22. The process of claim 13, wherein applying the intermediate layer is by
Laser-Arc.
23. The process of claim 22, wherein the Laser-Arc comprises a laser
controlled, pulsed vacuum arc.
24. The process of claim 13, wherein depositing the hard amorphous carbon
layer is by Laser-Arc.
25. The process of claim 24, wherein the Laser-Arc comprises a laser
controlled, pulsed vacuum arc.
26. The process of claim 13, wherein applying the intermediate layer and
depositing the hard amorphous carbon layer are by Laser-Arc in a same
arrangement.
27. The process of claim 13, wherein the wear-resistant edge layer
comprises:
a hard amorphous carbon layer;
an intermediate; and
a laser gas alloyed layer.
28. The process of claim 13, wherein the wear-resistant edge layer
comprises:
200 to 400 nm thick hard amorphous carbon layer;
50 to 200 nm thick intermediate layer; and
0.3 to 2.0 mm thick laser gas alloyed layer, the laser gas alloyed layer
comprising precipitated titanium nitride needles and having a hardness
between 600 HV0.1 and 1400 HV0.1.
29. A process for producing a wear-resistant edge layer on a substrate,
comprising:
forming a laser gas alloyed layer by melting tracks in a substrate surface
with a high power laser, the high power laser having a power density of
1.multidot.10.sup.4 W/cm.sup.2 to 2.multidot.10.sup.5 W/cm.sup.2, the
melting taking place in a reactive atmosphere having an oxygen partial
pressure less than 5 ppm, the reactive atmosphere comprising N.sub.2 and
Ar wherein a nitrogen content is 40% to 80%, an overlap level U being 0.5
to 0.9 where U(a-c)/a and where a is a track width and c is a track
spacing;
after melting the tracks, polishing the substrate to a surface roughness
less than or equal to 0.2 .mu.m;
cleaning the substrate with a high vacuum device by ion bombardment;
after cleaning the substrate, applying an intermediate layer by Laser-Arc;
and
after application of the intermediate layer, depositing a hard amorphous
carbon layer on the intermediate layer by Laser-Arc.
30. The process of claim 29, wherein the substrate comprises one of
titanium and tutanium alloy.
31. The process of claim 29, wherein the application of the intermediate
layer by Laser-Arc comprises a laser controlled, pulsed vacuum arc.
32. The process of claim 29, wherein the deposition of the hard amorphous
carbon layer by Laser-Arc comprises a laser controlled, pulsed vacuum arc.
33. The process of claim 29, wherein the application of the intermediate
layer by Laser-Arc and the deposition of the hard amorphous carbon layer
by Laser-Arc are performed with a same arrangement.
34. The process of claim 29, wherein the wear-resistant edge layer
comprises:
a hard amorphous carbon layer;
an intermediate layer; and
a laser gas alloyed layer.
35. The process of claim 29, wherein the wear-resistant edge layer
comprises:
200 to 400 nm thick hard amorphous carbon layer;
50 to 200 nm thick intermediate layer; and
0.3 to 2.0 mm thick laser gas alloyed layer, the laser gas alloyed layer
comprising precipitated titanium nitride needles and having a hardness
between 600 HV0.1 and 1400 HV0.1.
Description
BACKGROUND
1. Field of the Invention
The invention concerns edge layer refinement of functional components. The
present invention is useful in all functional components subjected to wear
caused by sliding friction made of titanium or its alloys, which are
stressed at operating temperatures below 500.degree. C., are subjected to
high surface pressure, and must have as low a coefficient of friction as
possible. The invention can be used particularly advantageously for the
protection of human implants, in particular with oscillating movements, as
well as aerospace sector components subjected to wear caused by sliding
friction.
2. Discussion of Background
Titanium is an excellent construction material whose high specific
strength, chemical resistance, and biocompatibility make titanium suitable
for various special applications. However, titanium's low resistance to
wear caused by sliding friction and its high coefficient of friction often
prevent a broader range of use.
It is known to produce very wear-resistant edge layers on titanium by laser
gas alloying (cf., e.g., H.W. Bergmann: "Thermochemical Treatment of
Titanium and Titanium Alloys by Laser Melting and Gas Alloying",
Zeitschrift fur Werkstofftechnik 16 (1985), p. 392-405).
Moreover, it is known to use laser gas alloying for the protection of joint
endoprostheses (DE 3 917 211). For this, the component is melted by the
laser beam to a depth of 0.1 to 0.7 mm, and nitrogen is simultaneously
blown into the melt. Because of the high affinity of titanium for reactive
gases, titanium nitride, which precipitates in the form of needles from
the melt, forms immediately. After solidification, the edge layer consists
of the metallic matrix of titanium with an altered .alpha./.beta.
proportion compared to the initial state, as well as very densely embedded
titanium nitride needles. The hardness of the edge layer is usually up to
1000 HV.
However, the shortcoming of such layers include a high coefficient of
friction and, moreover, strong abrasive wear with most mating bodies which
may be used. In this regard, the very hard titanium nitride needles
protrude out of the surface after the initial wear. Thus, the local stress
of the tribosystem is increased until the mating body is grooved and
simultaneously microscopic interlocking of the titanium nitride needles
with the mating body results, which increases the coefficient of friction.
Another shortcoming of these layers appears under loading in an
oxygen-containing atmosphere and especially under relatively high
temperatures and is expressed in that, particularly under deficient
lubrication conditions, a catastrophic failure of the frictional pair may
occur. The cause for this failure involves the metallic matrix between the
TiN needles havings a high affinity for oxygen.
In order to circumvent the negative effects of the TiN needles, in
particular for the human implant sector, a process for gas nitriding (U.S.
Pat. No. 5,326,362) has become known in which molecular nitrogen is
diffused into the region near the surface at a process temperature of
400.degree. C. to 704.4.degree. C. and forms a wear-resistant layer by
solution hardening. For this, the component is placed in a vacuum furnace,
evacuated to a pressure of 1.multidot.10.sup.-6 Torr, then filled with 1
atm nitrogen, heated to 537.7.degree. C.; the nitrogen pressure is
increased to 2 atm, and the component is nitrided at 593.3.degree. C. for
several hours. After completion of the treatment, the edge layer comprises
a 0.2 .mu.m-thick compound layer of titanium nitrides, titanium carbon
nitrides, titanium oxides, and titanium carbo-oxides and a diffusion layer
a few .mu.m thick. The titanium nitrides found in the compound layer are
significantly more finely dispersed than with laser gas alloying. Since
the compound layer forms a closed layer on the surface, the loading
capacity of the layer under an oxygen-containing atmosphere and elevated
temperatures is increased.
The shortcomings of this process include that the friction coefficient is
not adequately reduced and that the wear resistance is inadequate at high
contact pressures. The shortcomings result from the fact that, on the one
hand, the compound layer still comprises a very hard and not completely
flat titanium nitride needles, which interlock with the mating body and,
on the other hand, the underlying diffusion layer is too thin to be able
to resist high local stress for an adequately long time. The primary
reason for the latter is that with Hertz-calculated stresses with the
contact surfaces appearing in actual practice, the maximum stress lies
under the layer. Consequently, deformations may occur in the soft base
material, which result in a lifting of the brittle compound layer.
SUMMARY OF THE INVENTION
An object of an invention is to provide a biocompatible edge layer
structure which is resistant to wear caused by sliding and with a very low
sliding friction coefficient for titanium and its alloys and to propose a
process for its production.
Another object of the invention is to provide an edge layer structure which
has a greater hardness penetration depth by at least one order of
magnitude by making use of the high wear resistance of titanium nitride
and which contains no titanium nitride needles directly in its surface.
The invention is directed to a wear-resistant, mechanically highly
stressable, low friction edge layer structure for titanium or its alloys,
consisting of a laser gas alloyed layer with precipitated titanium nitride
needles.
The present invention is also directed to an intermediate layer, with which
a particularly good adhesion of the hard alorphous carbon layer is
achieved.
In addition, the present invention involves a process for production of an
edge layer structure with a low coefficient of friction and a very high
load carrying capacity.
In accordance with one aspect, the present invention is directed to a
wear-resistant edge layer for titanium and its alloys which can be
subjected to high loads and has a low coefficient of friction, comprising:
a hard amorphous carbon layer; an intermediate layer; and a laser gas
alloyed layer.
In accordance with another aspect, the present invention is directed to a
wear-resistant edge layer for titanium and its alloys which can be
subjected to high loads and has a low coefficient of friction, comprising:
200 to 400 nm thick hard amorphous carbon layer; 50 to 200 nm thick
intermediate layer; and 0.3 to 2.0 mm thick laser gas alloyed layer, the
laser gas alloyed layer comprising precipitated titanium nitride needles
and having a hardness between 600 HV0.1 and 1400 HV0.1.
The intermediate layer may comprise titanium or may consist of titanium.
In another aspect, the present invention is directed to a process for
producing a wear resistant edge layer on a substrate, comprising: forming
a laser gas alloyed layer by melting a surface of a substrate; applying an
intermediate layer by Laser-Arc; and depositing a hard amorphous carbon
layer on the intermediate layer by Laser-Arc.
In another aspect, the present invention is directed to a process for
producing a wear-resistant edge layer on a substrate, comprising: forming
a laser gas alloyed layer by melting tracks in a substrate surface with a
high power laser, the high power laser having a power density of
1.multidot.10.sup.4 W/cm.sup.2 to 2.multidot.10.sup.5 W/cm.sup.2, the
melting taking place in a reactive atmosphere having an oxygen partial
pressure less than 5 ppm, the reactive atmosphere comprising N.sub.2 and
Ar wherein a nitrogen content is 40% to 80%, an overlap level U being 0.5
to 0.9 where U=(a-c)/a and where a is a track width and c is a track
spacing; after melting the tracks, polishing the substrate to a surface
roughness less than or equal to 0.2 .mu.m; cleaning the substrate with a
high vacuum device by ion bombardment; after cleaning the substrate,
applying an intermediate layer by Laser-Arc; and after application of the
intermediate layer, depositing a hard amoi-phouts carbon layer on the
intermediate layer by Laser-Arc.
In one aspect, the application of the intermediate layer by Laser-Arc
comprises a laser controlled, pulsed vacuum arc.
In another aspect, the deposition of the hard amorphous carbon layer by
Laser-Arc comprises a laser controlled, pulsed vacuum arc.
In still another aspect, the application of the intermediate layer by
Laser-Arc and the deposition of the hard amorphous carbon layer by
Laser-Arc are performed with a same arrangement.
BRIEF DESCRIPTION OF THE DRAWINGS
The associated drawings depict the layer structure (FIG. 1) according to
the invention and the improvement in wear behavior (FIG. 2a) and friction
behavior (FIG. 2b).
DETAILED DESCRIPTION
The invention is explained in detail with reference to the following
exemplary embodiment.
EXAMPLE 1
A component 1 made of the alloy Ti6A14V with the dimensions
10.times.40.times.60 mm.sup.3 was provided on a flat side with a very
wear-resistant and low friction layer structure.
For this, the component 1, polished and cleaned of fatty residues by a
solvent, was positioned on the work table of a CNC machine. A special
bell-shaped shielding Gas attachment, into which an N.sub.2 /Ar mixture at
atmospheric pressure adjusted in a gas mixing station at the ratio N.sub.2
:Ar=60:40 or N.sub.2 :Ar=70:30 was blown in, was placed above the
component. The bell-shaped shielding attachment was designed such that it
was freely movable in three coordinate directions, and after a 90-sec
scavenging period, a residual oxygen content .ltoreq.3 ppm was guaranteed.
The laser power was 5 kW; the beam had a diameter of 3.4 mm on the
component; the feed rate was selected at 8 mm/s. The track spacing was
0.75 mm with a resultant track width of 4.5 mm . This yielded an overlap
level of 83.3%. After reaching the oxygen partial pressure <5 ppm, the
process of gas alloying was initiated by starting the CNC program and
releasing the laser beam. The gas alloyed layer 2 thus produced was 1.2 mm
deep, comprising titanium nitride needles, which were embedded in a
titanium matrix.
After cooling of the component, its surface was polished with a diamond
grinding wheel with a grain size of 125 .mu.m until a uniform surface with
a roughness .ltoreq.0.62 .mu.m was obtained. This is followed by grinding
with SiC paper P800 to P1200, until a roughness .ltoreq.0.12 .mu.m was
obtained.
Then, the surface of the component was cleaned in a vacuum chamber by ion
bombardment with argon ions. In the same chamber, there was an arrangement
for performance of the laser controlled, pulsed vacuum arc process (laser
arc process) to produce a hard amorphous carbon layer. The arrangement
includes a pulsed vacuum arc, the target material connected as the cathode
as well as a Q-switched Nd-YAG laser with a power density
>5.multidot.10.sup.8 W/cm.sup.2. The component was fastened in a substrate
holder.
The cylindrical cathode is bipartite, comprising a titanium and a graphite
cylinder.
A voltage inadequate to cause an arc discharge was applied between the
cathode and the anode. The laser was focused on the titanium cylinder and
turned on. Its pulses generated plasma clouds, each of which caused a
brief were discharge. Ti ions and atoms are deposited on the substrate.
After reaching the desired layer thickness of the intermediate layer 3, a
switch was made to the graphite cathode, and the hard amorphous carbon
layer 4 was deposited on the component. The layer deposited was 400 mm
thick and comprised a hard amorphous carbon film.
To determine wear resistance, the components were tested on a ball-on-disk
tribometer, wherein the ball was made of hard metal.
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